They're not all documented. For example, you won't find ARCHIVE_PATH, MARKETING_VERSION (the version string set in Xcode) in Naaff's or smorgan's answer. These 2 are very common pieces of information someone would need! Here's a list of all of them I got: https://gist.github.com/ben-xD/c063b0ca2c33684de1eb379bb9d6405d
How I got them
I found the best way was to print them using set, I just wrote this including a method to list all the environment variables available.
Add this to your run script (either Archive post run script, or your build phases run script, etc.):
#!/bin/sh
exec > ${PROJECT_DIR}/environment_variables.log 2>&1
set
Look in environment_variables.log and you'll see them all.